1. Field of the Invention
The present invention relates to a vehicle driving support device that appropriately avoids collision with an obstacle recognized ahead in a vehicle provided with an idle stop system or a vehicle, such as a hybrid vehicle, provided with an engine automatic stop function.
2. Description of Related Art
Recently, various collision avoidance control systems for vehicles have been developed and put to practical use. For example, Japanese Unexamined Patent Publication (JP-A) No. 2005-225453 describes a technique of a brake support system. In this technique, a time-to-collision (TTC) that is a value obtained by dividing a relative distance to an obstacle ahead of a vehicle by a relative speed to the obstacle is defined as a first parameter, an accelerator pedal release rate of a driver to the time-to-collision TTC upon an emergence of the obstacle ahead of the vehicle is defined as a second parameter, and a brake assist for a collision avoidance control is executed based upon a brake operation behavior characteristic map that illustrates a driver's brake operation behavior characteristic based upon information indicating a relationship between the first parameter and the second parameter.
On the other hand, a vehicle provided with an idle stop system or a vehicle, such as a hybrid vehicle, provided with an engine automatic stop function has been put into practical use in order to enhance fuel efficiency and to cope with environmental problems. When the brake support system described in JP-A No. 2005-225453 is applied to the vehicle having the engine automatic stop function, the brake assist system based upon a brake booster by a negative pressure of an engine cannot satisfactorily be operated during the stop of the engine, and hence, a desired safety performance might not be attained. In view of this, it is considered that the deterioration in the function of the negative-pressure brake booster during the stop of the engine is made up with an application of pressure by a pump of a brake driver, as a basic function of the vehicle having the engine automatic stop function. However, there arises a problem that, even if the pump is started after a driver's sudden braking operation is detected, a pressure-rising performance sufficient for the brake assist function cannot be attained, considering the responsiveness of a pump motor.